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Darkroom

Darkroom

A darkroom is a given space, usually a separate area in a building or a vehicle, that is made dark so as to allow photographers to use light-sensitive materials to develop photographs and film. Darkrooms were widely used in the late 19th and early to late 20th centuries (until about 1980) before color photography became universally popular. Using black and white film, amateur photographers could control every step of the photographic process and achieve much more finely tuned results at home for a reasonable price than with store-developed prints. Due to the relative complexity involved in processing colour film (see (C-41 process) and printing color photographs, and to the rise of first Polaroid technology and later digital photography, darkrooms are quickly decreasing in popularity amongst both the amateur and professional class. Nevertheless, darkrooms still enjoy considerable popularity on school campuses and are still used by many professional or hobbyist photographers.

The darkroom

The heart of every darkroom is the enlarger -- an optical apparatus that projects the image on a negative to a base. On the base, a sheet of photographic paper, typically either Resin-coated or fibre-based paper, is exposed. It is during this initial exposure that the photo can be modified, mostly by burning (giving more light to specific parts of an image by exposing it while blocking light to the rest) and/or dodging (reducing light to a specific part of an image by blocking light to it). The paper is then developed, rinsed or put into a stop bath, "fixed", then rinsed again and dried. Some darkrooms also have special print washers used to most thoroughly clean the paper. The darkroom does not have to be completely dark when making black and white prints. Red light or low-intensity orange or yellow light, known as safelights, make it possible to see when making prints without exposing the photographic paper. Color film, on the other hand, must be kept in complete darkness until the prints are properly fixed. Depending on personal preference, a darkroom may have a "paper-safe", which is a light-proof box to store photographic paper not in use as opposed to the light-proof bags that the paper comes packaged in, and a changing bag, which is a small bag with arm holes specially designed to be completely light proof and used to prepare film prior to developing. The key advantage of using a changing bag is that items used while loading or handling film are less likely to fall or be misplaced as they are enclosed in a small area.

External links

- [http://www.pedestrianx.com/darkroom Instructions for Setting Up A Darkroom in Your Home] Category:Photography

Photographer

Photography is the process of making pictures by means of the action of light. It involves recording light patterns, as reflected from objects, onto a sensitive medium through a timed exposure. The process is done through mechanical, chemical or digital devices commonly known as cameras. The word comes from the Greek words φως phos ("light"), and γραφις graphis ("stylus", "paintbrush") or γραφη graphê, together meaning "drawing with light" or "representation by means of lines" or "drawing."

Photographic image forming devices

Most commonly a camera or camera obscura is the image forming device and photographic film or a digital storage card is the recording medium, although other methods are available. For instance, the photocopy or xerography machine forms permanent images but uses the transfer of static electrical charges rather than photographic film, hence the term electrophotography. The rayographs published by Man Ray in 1922 are images produced by the shadows of objects cast on the photographic paper, without the use of a camera. And one can place objects directly on the glass of a scanner to produce pictures electronically. Photographers control the camera to expose the light recording material (usually film or a charge-coupled device) to light. After processing, this produces an image whose contents are acceptably sharp, bright and composed to achieve the objective of taking the photograph. The controls include:
- Focus
- Aperture of the lens
- Duration of exposure (or shutter speed)
- Focal length of the lens (telephoto, macro, wide angle, or zoom)
- Sensitivity of the medium to light intensity and color The controls are usually inter-related, for example brightness is aperture multiplied by shutter speed, and varying the focal length of the lens will allow greater control over the depth of field. Depth of field is the area of the image that is in focus. The larger the depth of field, the larger the area of the image that is in focus. The smaller the depth of field, the smaller the area that is in focus. A higher aperture setting, like f16 or f22, gives the photographer a smaller depth of field. A lower aperture setting, like f1.4 or f2.8, gives a larger depth of field.

Uses of photography

Photography can be classified under imaging technology and has gained the interest of scientists and artists from its inception. Scientists have used its capacity to make accurate recordings, such as Eadweard Muybridge in his study of human and animal locomotion (1887). Artists have been equally interested by this aspect but have also tried to explore other avenues than the photo-mechanical representation of reality, such as the pictorialist movement. Military, police and security forces use photography for surveillance, recognition and data storage.

History of photography

pictorialist pictorialist

Invention

Chemical photography

Projecting images onto surfaces has been done for centuries. The camera obscura and the camera lucida were used by artists to trace scenes as early as the 16th century. These early cameras did not fix an image in time; they only projected what was before an opening in the wall of a darkened room onto a surface. In effect, the entire room was turned into a large pinhole camera. Indeed, the phrase camera obscura literally means "darkened room," and it is after these darkened rooms that all modern cameras have been named. The first photograph is considered to be an image produced in 1826 by the French inventor Nicéphore Niépce on a polished pewter plate covered with a petroleum derivative called bitumen of Judea. It was produced with a camera, and required an eight hour exposure in bright sunshine. However, this process turned out to be a dead end and Niépce began experimenting with silver compounds based on a Johann Heinrich Schultz discovery in 1724 that a silver and chalk mixture darkens when exposed to light. Niépce, in Chalon-sur-Saône, and the artist Jacques Daguerre, in Paris, refined the existing silver process in a partnership. In 1833 Niépce died unexpectedly of a stroke, leaving his notes to Daguerre. While he had no scientific background, Daguerre made two pivotal contributions to the process. He discovered that by exposing the silver firstly to iodine vapour, before exposure to light, and then to mercury fumes after the photograph was taken, a latent image could be formed and made visible. By then bathing the plate in a salt bath the image could be fixed. In 1839 Daguerre announced that he had invented a process using silver on a copper plate called the Daguerreotype. A similar process is still used today for Polaroids®. The French government bought the patent and immediately made it public domain. Across the English Channel, William Fox Talbot had earlier discovered another means to fix a silver process image but had kept it secret. After reading about Daguerre's invention, Talbot refined his process, so that it might be fast enough to take photographs of people as Daguerre had done, and by 1840 he had invented the calotype process. He coated paper sheets with silver chloride to create an intermediate negative image. Unlike a daguerreotype, a calotype negative could be used to reproduce positive prints, like most chemical films do today. Talbot patented this process, which greatly limited its adoption. He spent the rest of his life in lawsuits defending the patent until he gave up on photography all together. But later this process was refined by George Eastman and is today the basic technology used by chemical film cameras. Hippolyte Bayard also developed a method of photography, but delayed announcing it and so was not recognized as its inventor. Hippolyte Bayard

Reference

- Coe, Brian. The Birth of Photography. Ash & Grant, 1976.

Social history

Popularization

The Daguerreotype proved popular as it responded to the demand for portraiture emerging from the middle classes during the Industrial Revolution. This demand, that could not be met in volume and in cost by oil painting, may well have been the push for the development of photography. But still daguerreotypes, while beautiful, were fragile and difficult to copy. A single photograph taken in a portrait studio could cost $1000 in 2005 dollars. Photographers also encouraged chemists to refine the process of making many copies cheaply, which eventually lead them back to Talbot's process. Ultimately, the modern photographic process came about from a series of refinements and improvements in the first 20 years. In 1884 George Eastman, of Rochester, New York, developed dry gel on paper, or film, to replace the photographic plate, so that a photographer no longer needed to carry boxes of plates and toxic chemicals around. In July of 1888 Eastman's Kodak camera went on the market with the slogan "You press the button, we do the rest". Now anyone could take a photograph and leave the dangerous portions of the process to others. Photography became available for the mass-market in 1901 with the introduction of Kodak Brownie. Very little has changed in chemical photography since then, though color film has become the standard, as well as automatic focus and automatic exposure. Digital recording of images is becoming increasingly prevalent, as digital cameras allow instant previews on LCD screens among other benefits, and the resolution of top of the range models has exceeded high quality 35mm film while lower resolution models have become affordable. For the enthusiast photographer processing black and white film, little has changed since the introduction of the 35mm film Leica camera in 1925.

Economic history

In the nineteenth century, photography developed rapidly as a commercial service. In the U.S. in 1890, the number of professional photographers was about the same as the number of accountants, artists, and dentists, respectively, and about ten times greater than the number of authors. End-user supplies of photographic equipment accounted for only about 20% of industry revenue. Several trends characterize the photographic industry from the end of the nineteenth century to the end of the twentieth century. The ratio of revenue from end-user photographic supplies to revenue from professional services rose by an order of magnitude. The prevalence of personal cameras and the ratio of end-user photographs rose closely in tandem with the prevalence of telephone and the telephone conversation minutes. However, the ratio of photographic industry revenue to telephone industry revenue dropped sharply.[http://www.galbithink.org/sense-s6.htm#wpp1] Given the development of new digital technologies for creating and sharing images, and of new communications devices, e.g. camera phones, understanding the economics of image use are becoming increasingly important for understanding the evolution of the communications industry as a whole. Resources Jenkins, Reese V. Images & Enterprise: Technology and the American Photographic Industry 1839-1925. Baltimore, The Johns Hopkins University Press, 1975. The book provides a fine overview of the economics of photography and is especially strong on the growth and development of the Eastman Kodak Company.

Color photography

Main article: color photography Color photography was explored throughout the 1800s. Initial experiments in color could not fix the photograph and prevent the color from fading. The first permanent color photo was taken in 1861 by the physicist James Clerk Maxwell. One of the early methods of taking color photos was to use three cameras. Each camera would have a color filter in front of the lens. This technique provides the photographer with the three basic channels required to recreate a color image in a darkroom or processing plant. Practical application of the technique was held back by the very limited colour response of early film; however, in the early 1900s, following the work of photo-chemists such as H. W. Vogel, emulsions with adequate sensitivity to green and red light at last became available. The first color film, Autochrome, thus did not reach the market until 1907; it was based on a 'screen-plate' filter made of dyed dots of potato starch. The first modern ('integrated tri-pack') color film, Kodachrome, was introduced in 1935 based on three colored emulsions. Most modern color films, except Kodachrome, are based on technology developed for Agfacolor (as 'Agfacolor Neue') in 1936. Instant color film was introduced by Polaroid in 1963. Color photography may form images as a positive transparency, intended for use in a slide projector or as color negatives, intended for use in creating positive color enlargements on specially coated paper. The latter is now the most common form of film (non-digital) color photography, owing to the introduction of automated photoprinting equipment.

Digital photography

Main article: digital photography digital photography Traditional photography was a considerable burden for photographers working at remote locations (such as press correspondents) without access to processing facilities. With increased competition from television, there was pressure to deliver their images to newspapers with greater speed. Photo-journalists at remote locations would carry a miniature photo lab with them, and some means of transmitting their images down the telephone line. In 1981, Sony unveiled the first consumer camera to use a CCD for imaging, and which required no film -- the Sony Mavica. While the Mavica did save images to disk, the images themselves were displayed on television, and therefore the camera could not be considered fully digital. In 1990, Kodak unveiled the DCS 100, the first commercially available digital camera. Its cost precluded any use other than photojournalism and professional applications, but commercial digital photography was born. Digital photography uses an electronic sensor such as a charge-coupled device to record the image as a piece of electronic data rather than as chemical changes on film. Some other devices, such as cell phones, now include digital photography features. In 10 years, digital cameras have become widespread consumer products. Digital cameras now outsell film cameras, and many include features not found in film cameras such as the ability to shoot video and record audio. Kodak announced in January 2004 that it would no longer produce reloadable 35-millimeter cameras after the end of that year. This was interpreted as a sign of the end of film photography. However, Kodak was at that time a minor actor on the reloadable film cameras market. The price of 35mm and APS compact cameras have dropped, probably due to direct competition from digital and the resulting growth of the offer of second-hand film cameras. However, "wet" photography may endure, as dedicated amateurs and skilled artists often prefer the use of traditional and familiar materials and techniques.

Commercial photography

The commercial photographic world is traditionally broken down to:
- Advertising photography: photographs done to illustrate a service or product. These images are generally done with an Advertising Agency, Design Firm or with an in-house Corporate design team.
- Editorial photography: photographs done to illustrate a story or idea within the context of a magazine. These are usually assigned by the magazine.
- Photojournalism: this can be considered a subset of Editorial. Photographs done in this context are accepted as a truthful documentation of a news story.
- Portrait and wedding photography: photographs done and sold directly to the end user of the images.
- Fine art photography: photographs created to fulfill a vision, and reproduced to be sold directly to the end user. The market for photographic services demonstrates the aphorism "one picture is worth a thousand words," which has an interesting basis in the history of photography. Magazines and newspapers, companies putting up Web sites, advertising agencies and other groups pay for photography. Many people take photographs for self-fulfillment or for commercial purposes. Organizations with a budget and a need for photography have several options: they can assign a member of the organization, hire someone, run a public competition, or obtain rights to stock photographs.

Terminology

Traditionally, the product of photography has been called a photograph. The term photo is a convenient abbreviation. Many people also call them pictures. In digital photography, the term image has begun to replace photograph. This term is neither more nor less correct than photograph, either in film or digital photography. (The term image is traditional in geometric optics.) Although not viewed by all photographers as true photography, digital photography in fact meets all requirements to be called such. Even though there are no chemical processes, a digital camera captures a frame of whatever it happens to be pointed at, which can be viewed later.

Photography as an art form

stock photographs settings can achieve unusual results]] During the twentieth century, both fine art photography and documentary photography became accepted by the English-speaking art world and the gallery system. In the USA, a small handful of curators spent their lives struggling to put it there, with Alfred Stieglitz, Edward Steichen and John Szarkowski, and Hugh Edwards the most prominent among them. Yet the aesthetics of photography is a matter that continues to be discussed regularly, especially in artistic circles. Is photography an art - or is it just the mechanical reproduction of an image? If photography is authentically art, what makes a photograph beautiful? Is there a kinship between the beauty of an Atget and a Rembrandt? The controversy began with the earliest images "written with light": [http://www.nicephore-niepce.com/pagus/pagus-bio.html Niépce], [http://www.rleggat.com/photohistory/history/daguerr.htm Daguerre], and others among the very earliest photographers were met with wonder, but some questioned if it was really art. Clive Bell in his classic essay "Art" states that only one thing can distinguish art from what is not art: "significant form." Bell wrote: "There must be some one quality without which a work of art cannot exist; possessing which, in the least degree, no work is altogether worthless. What is this quality? What quality is shared by all objects that provoke our aesthetic emotions? What quality is common to Sta. Sophia and the windows at Chartres, Mexican sculpture, a Persian bowl, Chinese carpets, Giotto's frescoes at Padua, and the masterpieces of Poussin, Piero della Francesca, and Cezanne? Only one answer seems possible - significant form. In each, lines and colors combined in a particular way, certain forms and relations of forms, stir our aesthetic emotions." [http://www.csulb.edu/~jvancamp/361r13.html Text of Bell's essay].

Aesthetic realism and photography

Clive Bell Others have since examined if this criterion be applied to photography. This question has been examined by the aesthetic realism understanding of beauty. Some of the most important writing on this subject is to be found on the web sites of Len Bernstein, [http://www.dienes-and-dienes.com/Atget.html Louis Dienes], [http://www.dienes-and-dienes.com/Cartier-Bresson.html Amy Dienes], and [http://www.mindspring.com/~davidmbernstein/Dorothea_Lange.html David M. Bernstein]: photographers and critics. Len Bernstein has described the [http://www.lenbernstein.com/ Aesthetic Realism understanding of photography as an art form] in essays which have been published for example in [http://www.apogeephoto.com/apr2001/bernstein4_2001.shtml Apogee Photo Magazine] and in [http://lenbernstein.com/Pages/RiisArticle.html Photographica World: The Journal of the Photographic Collectors Club of Great Britain]. On his web site he introduces the subject as follows: "When I began to photograph more than 25 years ago, I felt I found a way of expressing myself that met something so deep inside me that I wanted to do it for the rest of my life. Walking with my camera, the city streets seemed transformed - friendlier, more interesting - and I spent hours searching for dramatic situations, trying to capture the right moment. Looking through the viewfinder, what I saw had new value for me, boredom and loneliness seemed to vanish, and I wished I could feel that way all the time. And hoping to learn what made a photograph successful, I avidly studied the history and technique of photography. "My hopes were met when I first heard this magnificent statement by Eli Siegel, the American critic and founder of the philosophy Aesthetic Realism: [http://www.terraingallery.org/IsBeauty.html 'All beauty is a making one of opposites, and the making one of opposites is what we are going after in ourselves.'] This is the criterion for beauty that centuries of artists, philosophers, people in all walks of life, have searched for; the explanation of what makes a photograph good and how our personal questions are the questions of art - dignified and cultural! I've had the thrill of testing it in thousands of instances, from the first known photograph taken by Nicéphore Niépce in 1826-27 to the most modern work of today." [http://lenbernstein.com/PagesLargeImages/peopleparkbench.html For an online exhibition of Bernstein's photographs click here.] Likewise, important articles (referred to above) on photography as an art form, written from the Aesthetic Realism point of view, will be found on the David M. Bernstein web site [http://www.mindspring.com/~davidmbernstein/Dorothea_Lange.html "What Does a Person Deserve? The Answer Found in a Great Photograph"] and the "Dienes & Dienes" web site. See, for example Amy Dienes' [http://www.dienes-and-dienes.com/Cartier-Bresson.html "The Self Alone & The Self Going Out; or, Cartier-Bresson's Photo of a Leaping Man"]; Louis Dienes' [http://www.dienes-and-dienes.com/Atget.html "On a Photograph by Eugene Atget"] and his illustrated poem "Black and White," originally composed for his own exhibition of photographs, which begins: [http://www.dienes-and-dienes.com/Photographs-and-A-Poem-1st.html "The day black and white got a break..."] An often neglected form of art in photography is that of portrait photography. A portrait is the basic rendering of someone’s likeness. A good portrait photographer not only wants to capture the true likeness, but also the personality of the individual. The photographer needs to be proficient not only in the workings and setting of the camera, but also needs to understand form and lighting. Great lighting and positioning can make someone appear at their best form if used correctly. Lighting and camera placement can also aid in correcting defects such as shortening a nose, making someone appear slimmer, etc. In this form of art, portrait photography takes on many roles, and can help create various moods that the individual is seeking.

Reference

Tom Ang, Dictionary of Photography and Digital Imaging, The Essential Reference for the Modern Photographer (Argentum 2001)

Additional reading

- Freeman Patterson, Photography and The Art of Seeing, 1989, Key Porter Books, ISBN 1550130994.
- The Oxford Companion to the Photograph, ed. by Robin Lenman, Oxford University Press 2005

External links

- [http://www.digitalkb.com/digital_photography/knowledge_base/exposure/ Understanding Exposure and Digital Cameras (Image Sensors)]
- [http://www.dofmaster.com Depth of Field Calculators]
- [http://www.dpreview.com dpreview.com] digital camera reviews
- [http://www.photopermit.org PhotoPermit.Org] discussion on copyright law for photographers
- [http://www.luminous-landscape.com/ The Luminous Landscape] - photography techniques and camera reviews
- [http://photoinf.com/ Photography Composition Articles]
- [http://www.mccord-museum.qc.ca/en/keys/webtours/VQ_P3_2_EN.html Instant Memories] — the origins of amateur photography
- [http://www.mccord-museum.qc.ca/en/keys/webtours/VQ_P2_7_EN.html In the Eye of the Camera] — The limits of photography in 19th century
- [http://www.floridamemory.com/OnlineClassroom/photographic-processes/index.cfm Daguerreotype to Digital: A Brief History of the Photographic Process] From the State Library & Archives of Florida. Category:Arts Category:News Category:Photography ja:写真 th:การถ่ายภาพ

Light

Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. The three basic dimensions of light (i.e., all electromagnetic radiation) are:
- Intensity (or brilliance or amplitude), which is related to the human perception of brightness of the light,
- Frequency (or wavelength), perceived by humans as the color of the light, and
- Polarization (or angle of vibration), which is not perceptible by humans under ordinary circumstances. Due to wave-particle duality, light simultaneously exhibits properties of both waves and particles. The precise nature of light is one of the key questions of modern physics.

Visible electromagnetic radiation

Visible light is the portion of the electromagnetic spectrum between the frequencies of 380 THz (3.8×10¹⁴ hertz) and 750 THz (7.5×10¹⁴ hertz). The speed (

c

), frequency (

f

\nu

), and wavelength (

\lambda

) of a wave obey the relation: :

c = f~\lambda \,\!

Because the speed of light in a vacuum is fixed, visible light can also be characterised by its wavelength of between 400 nanometres (abbreviated 'nm') and 800 nm (in a vacuum). Light entering the eye is absorbed by light-sensitive pigments within the rod cells and cone cells in the retina, triggering a cascade of events that creates electrical nerve impulses that travel through the optic nerve to the brain, producing vision.

Speed of light

Although some people speak of the "velocity of light", the word velocity should be reserved for vector quantities, that is, those with both magnitude and direction. The speed of light is a scalar quantity, having only magnitude and no direction, and therefore speed is the correct term. The speed of light has been measured many times, by many physicists. The best early measurement is Ole Rømer's (a Danish physicist), in 1676. By observing the motions of Jupiter and one of its moons, Io, with a telescope, and noting discrepancies in the apparent period of Io's orbit, Rømer calculated a speed of 227,000 kilometres per second (approximately 141,050 miles per second). The first successful measurement of the speed of light using an earthbound apparatus was carried out by Hippolyte Fizeau in 1849. Fizeau directed a beam of light at a mirror several thousand metres away, and placed a rotating cog wheel in the path of the beam from the source to the mirror and back again. At a certain rate of rotation, the beam could pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau measured the speed of light as 313,000 kilometres per second. Léon Foucault used rotating mirrors to obtain a value of 298,000 km/s (about 185,000 miles/s) in 1862. Albert A. Michelson conducted experiments on the speed of light from 1877 until his death in 1931. He refined Foucault's results in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California. The precise measurements yielded a speed of 186,285 mile/s (299,796 km/s [1,079,265,600 km/h]). In daily use, the figures are rounded off to 300,000 km/s and 186,000 miles/s.

Refraction

All light propagates at a finite speed. Even moving observers always measure the same value of c, the speed of light in vacuum, as c = 299,792,458 metres per second (186,282.397 miles per second). When light passes through a transparent substance, such as air, water or glass, its speed is reduced, and it undergoes refraction. The reduction of the speed of light in a denser material can be indicated by the refractive index, n, which is defined as: :

n = \frac \;\!

Thus, n=1 in a vacuum and n>1 in matter. When a beam of light enters a medium from vacuum or another medium, it keeps the same frequency and changes its wavelength. If the incident beam is not orthogonal to the edge between the media, the direction of the beam will change. Refraction of light by lenses is used to focus light in magnifying glasses, spectacles and contact lenses, microscopes and refracting telescopes.

Optics

The study of light and the interaction of light and matter is termed optics. The observation and study of optical phenomena such as rainbows offers many clues as to the nature of light as well as much enjoyment.

Color and wavelengths

The different wavelengths are detected by the human eye and then interpreted by the brain as colors, ranging from red at the longest wavelengths of about 700 nm. (lowest frequencies) to violet at the shortest wavelengths of about 400 nm. (highest frequencies). The intervening frequencies are seen as orange, yellow, green, cyan, blue, and, conventionally, indigo.
indigo
The wavelengths of the electromagnetic spectrum immediately outside the range that the human eye is able to perceive are called ultraviolet (UV) at the short wavelength (high frequency) end and infrared (IR) at the long wavelength (low frequency) end. Some animals, such as bees, can see UV radiation while others, such as pit viper snakes, can see infrared light. UV radiation is not normally directly perceived by humans except in a very delayed fashion, as overexposure of the skin to UV light can cause sunburn, or skin cancer, and underexposure can cause vitamin D deficiency. However, because UV is a higher frequency radiation than visible light, it very easily can cause materials to fluoresce visible light. Cameras that can detect IR and convert it to light are called, depending on their application, night-vision cameras or infrared cameras. These are different from image intensifier cameras, which only amplify available visible light. When intense radiation (of any frequency) is absorbed in the skin, it causes heating which can be felt. Since hot objects are strong sources of infrared radiation, IR radiation is commonly associated with this sensation. Any intense radiation that can be absorbed in the skin will have the same effect, however.

Measurement of light

The following quantities and units are used to measure the quantity or "brightness" of light. Light can also be characterised by:
- amplitude,
- color, wavelength, or frequency, and
- polarization (or angle of vibration).

Light sources

polarization There are many sources of light. The most common light sources are thermal: a body at a given temperature emits a characteristic spectrum of black body radiation. Examples include sunlight (the radiation emitted by the chromosphere of the Sun at around 6,000 K peaks in the visible region of the electromagnetic spectrum), incandescent light bulbs (which emit only around 10% of their energy as visible light and the remainder as infrared), and glowing solid particles in flames. The peak of the blackbody spectrum is in the infrared for relatively cool objects like human beings. As the temperature increases, the peak shifts to shorter wavelengths, producing first a red glow, then a white one, and finally a blue color as the peak moves out of the visible part of the spectrum and into the ultraviolet. These colors can be seen when metal is heated to "red hot" or "white hot". The blue color is most commonly seen in a gas flame or a welder's torch. Atoms emit and absorb light at characteristic energies. This produces "emission lines" in the spectrum of each atom. Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames (light from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow light). Emission can also be be stimulated, as in a laser or a microwave maser. Acceleration of a free charged particle, such as an electron, can produce visible radiation: cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this. Particles moving through a medium faster than the speed of light in that medium can produce visible Cherenkov radiation. Certain chemicals produce visible radiation by chemoluminescence. In living things, this process is called bioluminescence. For example, fireflies produce light by this means, and boats moving through water can disturb plankton which produce a glowing wake. Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. This is used in fluorescent lights. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example of this. This mechanism is used in cathode ray tube televisions. Certain other mechanisms can produce light:
- scintillation
- scintillator
- electroluminescence
- sonoluminescence
- triboluminescence
- radioactive decay
- particle-antiparticle annihilation

Theories about light

Early Greek ideas

In 55 BC Lucretius, continuing the ideas of earlier atomists, wrote that light and heat from the Sun were composed of minute particles. Ptolemy also wrote about the refraction of light.

10th century optical theory

The scientist Abu Ali al-Hasan ibn al-Haytham (965-c.1040), also known as Alhazen, developed a broad theory that explained vision, using geometry and anatomy, which stated that each point on an illuminated area or object radiates light rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. The other rays strike at different angles and are not seen. He used the example of the pinhole camera, which produces an inverted image, to support his argument. Alhazen held light rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy's theory of the refraction of light. Alhazen's work did not become known in Europe until the late 16th century.

The 'plenum'

René Descartes (1596-1650) held that light was a disturbance of the plenum, the continuous substance of which the universe was composed. In 1637 he published a theory of the refraction of light which wrongly assumed that light travelled faster in a denser medium, by analogy with the behaviour of sound waves. Descartes' theory is often regarded as the forerunner of the wave theory of light.

Particle theory

Pierre Gassendi (1592-1655), an atomist, proposed a particle theory of light which was published posthumously in the 1660s. Isaac Newton studied Gassendi's work at an early age, and preferred his view to Descartes' theory of the plenum. He stated in his Hypothesis of Light of 1675 that light was composed of corpuscles (particles of matter) which were emitted in all directions from a source. One of Newton's arguments against the wave nature of light was that waves were known to bend around obstacles, while light travelled only in straight lines. He did, however, explain the phenomenon of the diffraction of light (which had been observed by Francesco Grimaldi) by allowing that a light particle could create a localised wave in the aether. Newton's theory could be used to predict the reflection of light, but could only explain refraction by incorrectly assuming that light accelerated upon entering a denser medium because the gravitational pull was greater. Newton published the final version of his theory in his Opticks of 1704. His reputation helped the particle theory of light to dominate physics during the 18th century.

Wave theory

In the 1660s, Robert Hooke published a wave theory of light. Christian Huygens worked out his own wave theory of light in 1678, and published it in his Treatise on light in 1690. He proposed that light was emitted in all directions as a series of waves in a medium called the aether. As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium. The wave theory predicted that light waves could interfere with each other like sound waves (as noted in the 18th century by Thomas Young), and that light could be polarized. Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colors were caused by different wavelengths of light, and explained color vision in terms of three-colored receptors in the eye. Another supporter of the wave theory was Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory. Later, Fresnel independently worked out his own wave theory of light, and presented it to the Académie des Sciences in 1817. Simeon Denis Poisson added to Fresnel's mathematical work to produce a convincing argument in favour of the wave theory, helping to overturn Newton's corpuscular theory. The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt by the Michelson-Morley experiment. Newton's corpuscular theory implied that light would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Léon Foucault, in 1850. His result supported the wave theory, and the classical particle theory was finally abandoned.

Electromagnetic theory

In 1845, Faraday discovered that the angle of polarisation of a beam of light as it passed through a polarising material could be altered by a magnetic field, an effect now known as Faraday rotation. This was the first evidence that light was related to electromagnetism. Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the aether. Faraday's work inspired James Clerk Maxwell to study electromagnetic radiation and light. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation: he first stated this result in 1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism, which contained a full mathematical description of the behaviour of electric and magnetic fields, still known as Maxwell's equations. The technology of radio transmission was, and still is, based on this theory. The constant speed of light predicted by Maxwell's equations contradicted the mechanical laws of motion that had been unchallenged since the time of Galileo, which stated that all speeds were relative to the speed of the observer. A solution to this contradiction would later be found by Albert Einstein.

Particle theory revisited

The wave theory was accepted until the late 19th century, when Einstein described the photoelectric effect, by which light striking a surface caused electrons to change their momentum, which indicated a particle-like nature of light. This clearly contradicted the wave theory, and for years physicists tried in vain to resolve this contradiction.

Quantum theory

In 1900, Max Planck described quantum theory, in which light is considered to be as a particle that could exist in discrete amounts of energy only. These packets were called quanta, and the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton. A photon has an energy, E, proportional to its frequency, f, by :

E_f = hf = \frac \,\!

where h is Planck's constant,

\lambda

is the wavelength and c is the speed of light. As it originally stood, this theory did not explain the simultaneous wave-like nature of light, though Planck would later work on theories that did. The Nobel Committee awarded Planck the Physics Prize in 1918 for his part in the founding of quantum theory.

Wave-particle duality

The modern theory that explains the nature of light is wave-particle duality, described by Albert Einstein in the early 1900s, based on his work on the photoelectric effect and Planck's results. Einstein determined that the energy of a photon is proportional to its frequency. More generally, the theory states that everything has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. The particle nature is more easily discerned if an object has a large mass, so it took until an experiment by Louis de Broglie in 1924 to realise that electrons also exhibited wave-particle duality. Einstein received the Nobel Prize in 1921 for his work with the wave-particle duality on photons, and de Broglie followed in 1929 for his extension to other particles.

A light wave

1929 that oscillate perpendicular to each other and to the direction of motion (a transverse wave).]] The electric and magnetic fields are perpendicular to the direction of travel and to each other. This picture depicts a very special case, linearly polarized light. See Polarization for a description of the general case and an explanation of linear polarization. While these relations of the electric and magnetic fields are always true, the subtle difference in the general case is that the direction and amplitude of the magnetic (or electric) field can vary, in one place, with time, or, in one instant, can vary along the direction of propagation.

Photography

Photographic image forming devices

Uses of photography

History of photography

pictorialist pictorialist

Invention

Chemical photography

Reference

- Coe, Brian. The Birth of Photography. Ash & Grant, 1976.

Social history

Popularization

Economic history

Color photography

Digital photography

Commercial photography

Terminology

Photography as an art form

Aesthetic realism and photography

Reference

Tom Ang, Dictionary of Photography and Digital Imaging, The Essential Reference for the Modern Photographer (Argentum 2001)

Additional reading

- Freeman Patterson, Photography and The Art of Seeing, 1989, Key Porter Books, ISBN 1550130994.
- The Oxford Companion to the Photograph, ed. by Robin Lenman, Oxford University Press 2005

External links

Photographic film

Photographic film is a sheet of plastic (polyester, celluloid (nitrocellulose) or cellulose acetate) coated with an emulsion containing light-sensitive silver halide salts (bonded by gelatin) with variable crystal sizes that determine the sensitivity and resolution of the film. When the emulsion is subjected to controlled exposure to light (or other forms of electromagnetic radiation such as X-rays), it forms a latent (invisible) image. Chemical processes can then be applied to the film to create a visible image, in a process called film developing. In black-and-white photographic film there is usually one layer of silver salts. When the exposed grains are developed, the silver salts are converted to metallic silver, which block light and appear as the black part of the film negative. Color film uses at least three layers. Dyes added to the silver salts make the crystals sensitive to different colors. Typically the blue-sensitive layer is on top, followed by the green and red layers. During development, the silver salts are converted to metallic silver, as with black and white film. The by-products of this reaction form colored dyes. The silver is converted back to silver salts in the bleach step of development. It is removed from the film in the fix step. Some films, like Kodacolor II, have as many as 12 emulsion layers, with upwards of 20 different chemicals in each layer. Because photographic film was ubiquitous in the production of motion pictures, or movies, these are also known as films.

Film basics

There are two primary types of photographic film:
- Print film, when developed, turns into a negative with the colors (or black and white values, in black and white film) inverted. This type of film must be "printed" — either projected through a lens or placed in contact — to photographic paper in order to be viewed as intended. Print films are available in both black & white and color.
- Color reversal film after development is called a transparency and can be viewed directly using a loupe or projector. Reversal film mounted with plastic or cardboard for projection is often called a slide. It is also often marketed as "slide" film. This type of film is often used to produce digital scans or color separations for mass-market printing. Photographic prints can be produced from reversal film, but the process is expensive and not as simple as that for print film. Black and white reversal film exists, but is uncommon — one of the reasons reversal films are popular among professional photographers is the fact that they are generally superior to print films with regards to color reproduction. (Conventional black and white negative stock can be reversal- processed, to give 'black & white slides', and kits are available to enable this to be done by home-processors - however, the gamma required for an effective slide is high, and more easily achieved with a slower film like Pan-F). In order to produce a usable image, the film needs to be exposed properly. The range of tones that a given film can accurately record is called its exposure latitude. Color print film generally has better exposure latitude than other types of film. Additionally, because color print film must be printed to be viewed, some after-the-fact correction of the exposure can be made during the printing process. The concentration of dyes or silver salts remaining on the film after development is referred to as density. A dark image on the negative is of higher "density" than a more transparent image. If part of the image exceeds the maximum density possible for a print film, then it is overexposed and will appear as featureless white on the print. Likewise, if part of an image is beneath the minimum density possible on a film, the area will appear as featureless black. Some photographers use their knowledge of these limits to determine the optimum exposure for a photograph; for one example, see the Zone system. Most automatic cameras instead try to achieve a particular average density. Film speed describes a film's overall sensitivity to light. The international standard for rating film speed is the ISO scale (also known as ASA, since it it was initially developed by the American Standards Association). Common film speeds include ISO 25, ISO 50, ISO 64, ISO 100, ISO 160, IS0 200, ISO 400, ISO 800, ISO 1600, and ISO 3200. Consumer print films are usually in the ISO 100 to ISO 800 range. Some films, like Kodak's Technical Pan, are not ISO rated and therefore careful examination of the film's properties must be made by the photographer before exposure and development. ISO 25 film is very "slow", so it requires much more exposure to produce a usable image than ISO 800 film. Films of ISO 800 and greater (referred to as "fast" films) are thus better suited to low-light situations and action shots. The benefit of slower films is that it usually has finer grain and better colour rendition than fast film. Professional photographers usually seek these qualities, and therefore require a tripod to stabilize the camera for a longer exposure. Grain size refers to the size of the silver crystals in the emulsion. The smaller the crystals, the finer the detail in the photo. A film with a particular ISO rating can be pushed to behave like a film with a higher ISO — that is, exposed for a shorter period of time than would normally be used. In order to do this, the film must be developed for a longer amount of time than usual. This procedure is usually only performed by the photographer who does their own development, or by professional-level photofinishers. More rarely, a film can be pulled to behave like a "slower" film.

History of film

Pioneering work on the light sensivity of films was done by Hurter & Driffield from 1876 onwards; this work enabled the first quantitative measure of film speed to be devised. The first flexible photographic film was made by Eastman Kodak in 1885. This "film" was coated on paper. The first transparent plastic film was produced in 1889. Before this, glass photographic plates were used, which were far more expensive and cumbersome, albeit also of better quality. Early photography in the form of daguerreotypes did not use film at all.

Special films

Instant photography, as popularised by Polaroid, uses a special type of camera and film that automates and integrates development, without the need of further equipment or chemicals. This process is carried out immediately after exposure, as opposed to regular film, which is developed afterwards and requires additional chemicals. See instant film. Specialty films exist for recording non-visible portions of the electromagnetic spectrum. These films are usually designed to record either ultraviolet or infrared light. These films can require special equipment; for example, most photographic lenses are made of glass and will therefore filter out most ultraviolet light. Instead, expensive lenses made of quartz must be used. Film sensitized to X-ray radiation is commonly used for medical imaging, and personal monitoring.

Common sizes of film

See also Film format.
- 135 (popularly known as "35mm")
- APS (Advanced Photo System)
- 110
- 127
- 120/220 (for use in medium format photography)
- Sheet film (for use in large format photography)
- Motion picture films: 8mm, 16mm, 35mm and 70mm

Companies that manufacture photographic film

- Agfa-Gevaert
- Efke
- Foma
- Forte
- Ferrania
- Fujifilm
- Ilford
- Imation (Spin-off company of 3M has since sold off film production to Kodak.)
- Kodak
- Konica
- Lucky
- Maco
- Orwo
- Perutz (film)
- Polaroid
- ProClick
- Solaris (film)
- Svema
- Tasma
- Tura (film) Film manufacturers commonly make film that is branded by other companies. Modern films have bar codes on the edge of the film which can be read by a bar code reader. This is because film is sometimes processed differently according to specifications of the film, determined by its manufacturer; the bar code is entered into the computer printer before the film is printed. To establish the OEM, read the bar code printed on the cassette. Divide the long number by 16 and record the number before the decimal, then multiply the number after the decimal by 16, this could give you a result such as 18 and 2. The first number is known as the PRODUCT (film manufacturer) and the second number as the MULTIPLIER (speed of the film ISO). In the previous example, 18 identifies 3M as the manufacturer and 2 means it is 200 ISO:
- 3M = 18
- Agfa = 17 or 49
- Kodak = 80, 81, 82 or 88

19th century

:Alternative meaning: Nineteenth Century (periodical) The 19th century lasted from 1801 to 1900 in the Gregorian calendar (using the Common Era system of year numbering). Historians sometimes define a "Nineteenth Century" historical era stretching from 1815 (The Congress of Vienna) to 1914 (The outbreak of the First World War).

Europe

For Europe, the period is marked with revolution, social upheaval, and the emergence of a united conservatism from the monarchs of Europe in response to the emerging republican firestorm spreading from revolutionary France. There were many revolutions in Europe in 1848. Furthermore, the later end of the century was dominated by what many call the New Imperialism, which was the rapid aquisition of colonies worldwide by European powers, most noteworthy is the Scramble for Africa. Many countries in Europe underwent an Industrial Revolution, especially Britain and Germany, that spread elsewhere by the end of the century, with factories and railway lines built all over the continent. The start of the 19th century there was a struggle between France and Britain and their allies for control of Europe and the world during the Napoleonic Wars, with Napoleon being finally defeated at Waterloo in 1815. During the rest of the century, the British empire became the largest and most powerful empire in history, during the period known as the Pax Britannica.

Americas

In the Americas, the United States slowly grew economically, militarily, and politically, but nevertheless faced dramatic changes domestically, best seen in the Civil War, the end of slavery, and the expansion across the American continent known as Manifest Destiny. Industrially, America will explode following the Civil War, and would eventually begin expansion outward across the Pacific Ocean and in Latin America.

Other countries

For the rest of the world, there were few places not influenced by the West in some fashion, whether through colonialism, imperialism, or war. European powers gained increasing influence in China, where Qing control had weakened, and wars were fought by the western powers against China, such as the first and the second Opium wars and Sino-French War. Japan, which was forcibly opened to Western trade, began a rapid industrialisation. Africa which was largely free from European control at the start of the century, was almost completely dominated by Europe at the end of it, with the Scramble for Africa in the 1880s and 1890s. Large European settlement, especially British, of colonies such as Australia, New Zealand and the Cape Colony continued during the nineteenth century.

Darkroom

The darkroom

See also

External links

Photographer

Photographic image forming devices

Uses of photography

History of photography

Invention

Chemical photography

Reference

Social history

Popularization

Economic history

Color photography

Digital photography

Commercial photography

Terminology

Photography as an art form

Aesthetic realism and photography

Reference

Additional reading

See also

Basic topics in photography

Photographers

Photographs

Historical

Techniques

Photographic products

Other

External links

Light

Visible electromagnetic radiation

Speed of light

Refraction

Optics

Color and wavelengths

Measurement of light

Light sources

Theories about light

Early Greek ideas

10th century optical theory

The 'plenum'

Particle theory

Wave theory

Electromagnetic theory

Particle theory revisited

Quantum theory

Wave-particle duality

A light wave

See also

Photography

Photographic image forming devices

Uses of photography

History of photography

Invention

Chemical photography

Reference

Social history

Popularization

Economic history

Color photography

Digital photography

Commercial photography

Terminology

Photography as an art form

Aesthetic realism and photography

Reference

Additional reading

See also

Basic topics in photography

Photographers

Photographs

Historical

Techniques

Photographic products

Other

External links

Photographic film

Film basics